Tektites (from Greek tektos, molten) are natural glass objects, up to a few centimetres in size, which — according to most scientists — have been formed by the impact of large meteorites on Earth's surface. Tektites are among the "driest" rocks, with an average water content of 0.005%. This is very unusual, as most if not all of the craters where tektites may have formed were underwater before impact. Also, partially melted zircons have been discovered inside a handful of tektites. This, along with the water content, suggests that the tektites were formed under phenomenal temperature and pressure not normally found on the surface of the Earth.